Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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872
FXUS63 KDVN 200455
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1155 PM CDT Tue Sep 19 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 327 PM CDT Tue Sep 19 2017

18Z surface data had an implied frontal boundary from near KCMI, to
KLWD, to KMBG. Dew points north and east of the front were in the
50s to mid 60s. South and west of the front dew points were in the
upper 60s and some lower 70s.

&&

.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 327 PM CDT Tue Sep 19 2017

Through sunset, quiet and warm conditions are expected across the
area. The still dissipating clouds from this mornings fog have
helped to hold down temperatures a little.

This evening, quiet and dry conditions are expected as the warm
front slowly starts moving north. Moisture moving into the area
aloft should allow a slow increase in clouds. Forcing is weak but as
the air aloft becomes unstable, some elevated showers are possible
over the northwest parts of the area. However, due to the deep layer
of drier air at the surface only some sprinkles may reach the ground.

After midnight, the warm front will move through the area. Stronger
forcing moving in from the northwest will lift the increasingly
moist and unstable air to generate elevated showers and some
thunderstorms in the pre-dawn hours north of I-80 and mainly west of
the Mississippi.

Wednesday morning, the nocturnal elevated convection will slowly
dissipate during the morning. Increasing southerly flow will bring
humid air into the area and push heat index readings into the 85 to
90 degree range by mid-day.

Wednesday afternoon the cold front moves into eastern Iowa during
peak heating. Isolated showers and thunderstorms are expected to
slowly develop along the weak convergence of the front.

By late afternoon a new line of showers and thunderstorms is
expected to develop along the Mississippi in what the models suggest
is a pre-frontal trof. This pre-frontal trof looks to be the main
focus for storms to grow upscale into a narrow line line that will
probably have embedded strong storms. If severe storms develop late
Wednesday afternoon, they probably will be isolated with the
slightly better risk being east of the Mississippi.

Temperatures may approach records Wednesday for Burlington and
Moline. Refer to the climate section for specific numbers.

.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 327 PM CDT Tue Sep 19 2017

A return to warmer temperatures are forecast for the long term with
a couple chances of precipitation as the pattern returns to a summer
like approach.  Ongoing showers and storms should start the long
term period Wednesday night before the cold front mixes and shifts
north as a warm front entrenches north of the area.  Towards the
end of period a long wave trough is forecast to move into the area.

At the beginning of the period, ongoing showers and thunderstorms
seem plausible.  Sufficient instability with growing deep layer
shear may lead to strong and even severe thunderstorms.  Main
uncertainty in thunderstorm strength remains whether or not the
shear will be in place with any instability.  At this time it appears
that storms closest to the front will have a better chance of being
severe.

Past this, a warm up with guidance forecasting near record highs
with temperatures in the upper 80s to low 90s.  The GEM appears to
be outlier on the high end of temps with forecast highs above the
records.  Think that this might be pulling our overall blends higher
than the rest of the guidance.  MOSguide seems to be the lowest of
all guidance.  That said, there remains a difference between
MOSguide and GEM of nearly 8 degrees.  With that large of a spread,
confidence in temperature forecasts are lower than average.

Towards the end of the period, Dprog DT of the GFS on Tuesday
suggests a front across the area and a chance for precip.  Think
these chances will remain, however with blocking pattern, I`m not
too confident on the actual timing of the next chance for precip.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
ISSUED AT 1146 PM CDT Tue Sep 19 2017

VFR conditions will prevail through this TAF period. LLWS is a
concern at the terminals tonight into Wednesday morning, but is
forecast to be strongest at KCID/KDBQ. So included in TAFs at
these two terminals.

A cold front will slowly approach E Iowa/NW Illinois late
Wednesday afternoon into the night. At this time, the best
chances for periods of showers and thunderstorms through
06z/Thursday are at KDBQ. Since this is at the end of the TAF
period, mentioned threat for storms in PROB30 groups. Uttech

&&

.CLIMATE...
ISSUED AT 327 PM CDT Tue Sep 19 2017

Record Highs for September 20...

Moline.........92 in 1931
Cedar Rapids...93 in 1931
Dubuque........92 in 1895
Burlington.....93 in 1940

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...Gibbs
AVIATION...Uttech
CLIMATE...08



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